Overview of bone biology in the egg-laying hen

Abstract

In young pullets, long bones elongate by endochondral growth. Growth plate chondrocytes proliferate, then hypertrophy, and are replaced by osteoblasts that form a network of trabecular bone. This bone is gradually resorbed by osteoclasts as the bone lengthens. Long bones widen, and flat bones are formed, by intramembranous ossification in which cortical bone formation by osteoblasts in the periosteal layer is accompanied by osteoclastic resorption at the inner endosteal surface. Growth of structural trabecular and cortical bone types continues up to the onset of sexual maturity in pullets. At this point, the large surge in estrogen changes the function of osteoblasts to forming medullary bone rather than structural bone. Medullary bone is a woven bone that acts as a labile source of calcium for eggshell formation. It lines structural bone and also occurs as spicules within the marrow cavity. It has little inherent strength but can contribute to fracture resistance. Osteoclasts resorb both medullary and structural bone so that during the period the hen remains in reproductive condition there is a progressive loss of structural bone throughout the skeleton, which is characteristic of osteoporosis. The increasing fragility of the bones makes them more susceptible to fractures. The dynamics of bone loss can be affected by a number of nutritional, environmental, and genetic factors. If the hen goes out of reproductive condition, estrogen levels fall, osteoblasts resume structural bone formation, and skeletal regeneration can take place.

Limestone particle size and artificial light for laying hens in the second laying cycle

“…Moreover, we can infer that the similarity in the results obtained for bone characteristics of poultry depending on the lighting program effects is due to the absence of significant differences in feed consumption and egg production of poultry subjected to the lighting programs tested, since it has been reported that bone quality of laying hens depends upon the level of production (Silversides et al, 2006), intensity of bone resorption during the laying phase (Whitehead, 2004) and the calcium availability for eggshell formation (Fleming et al, 1998;Saunders-Blades et al, 2009).…”

“…As laying hens age, there is a drop in the eggshell quality due to factors such as lower calcium retention and increased egg weight without increasing the shell weight, in addition to the common bone fragility at the end of the production cycle (Whitehead, 2004;Murata et al, 2009). Almeida Paz et al (2009) reported that regardless of the dietary calcium level, the laying hens mobilize the minerals from bones for eggshell formation, so bone quality reduces as they grow old.…”

Neither season nor sex affects the cost of terrestrial locomotion in a circumpolar diving duck: the common eider (Somateria mollissima)

“…This theory is not challenged by our results as no sex differences in pelvic morphology or energetics were found. Furthermore, the reduction in bone fracture resistance by the provision of calcium for egg production has also been suggested as a potential limitation on female terrestrial locomotion (Whitehead 2004;Lees et al 2011). It may be that female hindlimbs are weakened during, and just after the egg-laying period; however, this is likely to be of more importance to birds that spend more time locomoting terrestrially than the eiders.…”

A Review of Laying Hens' Behavior

“…심각할 경우 폐 사에 이르며 (Whitehead, 2004;Whitehead and Fleming, 2000), McCoy et al(1996)는 케이지에서 사육되던 중 폐사한 닭의 35%가 골다공증을 앓고 있었던 것으로 보고한 바 있다. 케 이지는 산란계가 날개를 펼칠 수 있을 만큼 공간이 넉넉하지 못하기 때문에 특히 날개 부근의 골격근이 매우 약해진다.…”

“…그러나 일부 학자 들은 전자가 더 적합한 용어라고 주장하고 있다 (Lindberg and Nicol, 1997;van Liere and Wiepkema, 1992 (Rodenburg et al;2004;Rushen, 1982;Wood-Gush, 1971 Van Liere DW, Wiepkema PR 1992 Effects of long-term de-…”